This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A toy popgun can be easily made of two blocks of hard wood, 1/2 in. thick; a joint of bamboo, about 7/8 in. in diameter and 6 in. long; a small hinge, a piece of spring steel, 1/2in. wide and 1 in. long, and a piece of soft wood for the plunger.
The plunger A is cut to fit snugly, yet so it will move easily in the piece of bamboo B. One of the blocks of hard wood, C, is bored to fit, one end of the bamboo, the other block has A 1/4-in. hole bored, to center the hole in the first block. The two blocks are hinged and the spring latch attached as shown in the sketch. The spring has a hole drilled so it can be fastened with a screw to the outer block, and a slot cut in the other end to slip over a staple driven into the block C. A piece of paper, D, is placed in between the blocks while the plunger A is out at the end of the bamboo. A quick pressure on the plunger A will cause the paper D to break out through the small opening with a loud pop. - Contributed by Paul H. Burkhart, Blue Island, Ill.
Ill: Detail of Popgun, Showing the Parts Assembled and Position of the Paper